There are many aqueous industrial systems which require that various materials remain in a soluble, or suspended, or dispersed state. Typical aqueous systems include, for example, boiler water or steam generating systems, cooling water systems, gas scrubbing systems, pulp and paper mill systems, desalination systems, and downhole systems encountered during the production of gas, oil, and geothermal wells. In many cases, water contains (either naturally or by contamination) ingredients, such as inorganic salts, which can cause accumulation, deposition, and fouling problems. These salts are formed by the reaction of metal cations, such as calcium, magnesium or barium, with inorganic anions such as phosphate, carbonate and sulfate. These salts have low solubilities in water and as their concentration in solution increases, or as the pH or temperature of the water containing them increases, these salts tend to precipitate from solution, crystallize and form hard deposits of scale on surfaces. Scale formation is a problem in heat transfer devices, boilers, secondary oil recovery wells, automatic dish washers and on substrates washed with such hard waters.
Many cooling water systems constructed from carbon steel, including industrial cooling towers and heat exchangers, experience corrosion problems. Corrosion is combated by the addition of various inhibitors such as orthophosphate compounds and/or zinc compounds. The addition of phosphates, however, adds to the formation of highly insoluble phosphate salts such as calcium phosphate. The addition of zinc compounds can also lead to the precipitation of insoluble salts such as zinc hydroxide and zinc phosphate. Other inorganic particulates, such as mud, silt and clay, are commonly found in cooling water. These particulates tend to settle onto surfaces and thereby restrict water flow and heat transfer unless they are effectively dispersed.
The stabilization of aqueous systems containing scale forming salts and inorganic particulates involves one or a combination of mechanisms. Dispersion of the precipitated salt crystals is a stabilization mechanism believed to be the result of the adsorption of the inhibitor onto precipitated crystals. The adsorption of the inhibitor can also be used to stabilize the system by facilitating the dispersion and subsequent removal of other suspended particulates, such as mud, silt and clay, and metals such as iron and zinc and their insoluble salts, from aqueous systems. Another stabilization mechanism involves the ability of the inhibitor to interfere with and distort the crystal structure of the scale, thereby making the scale less adherent to surfaces or other forming crystals or existing particulates.
Many different synthetic water-treatment polymers have been employed in a wide range of water-treatment applications as dispersants for particulate matter, inhibitors of mineral scale formation and deposition, and corrosion inhibitors. Polymers containing carboxylic acid and/or sulfonic acid functionality have been found to be particularly useful.
The water-treatment polymer is added to the aqueous system in a predetermined concentration which is effective to inhibit the formation and deposition of mineral scale and to inhibit corrosion. Once the water-treatment polymers have been introduced into the aqueous systems, the concentration of the polymers in the aqueous system must be monitored by some means in order that the amount of polymer present in the system can be maintained at the predetermined concentration.
There have been many methods reported which have been used to monitor the concentration of the water-treatment polymers. For instance, inert fluorescent tracers such as 2-naphthalenesulfonic acid are used. The emissivity of a sample of water is compared to a standard solution of the fluorescent tracer. However, this method requires calibration of the emissivity instrumentation and compensation for "background fluorescence" which may be present in the system water or the water-treatment polymer.
Polymers "tagged" with chemically-bound ultraviolet/visible light absorbing chromophores and fluorescent units have also been used to monitor and control the level of the water-treatment polymer. However, like the aforementioned method, emissivity testing, instrumentation and the calibration thereof, as well as background fluorescence, complicate the method.
Methods for the colorimetric determination of polycarboxylates and/or sulfonates in aqueous systems are also known. The method comprises adjusting the pH of a portion of the aqueous solution to a predetermined value. The exact pH value is dependent on whether one is testing for sulfonates or carboxylates. A metachromatic dye is added to the solution in amounts effective for interaction of the dye with the carboxylate groups or the sulfonate groups. The absorbance is then measured and compared to absorbencies of standard samples.
It would be desirable to develop a water-treatment polymer which is readily detectable at concentrations of less than 100 parts per million and to develop methods for detecting the water-treatment polymer at such concentrations. The polymers and methods should not involve the use of fluorescent tracers or dyes. Additionally, the performance of the water-treatment polymers themselves should not be adversely affected. The method should be able to be conducted in a relatively short period of time, preferably without the need for expensive and/or sensitive instrumentation or standardization methods. The method should be accurate in concentrations of less than 100 ppm.